'\"
'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH Tcl_LinkVar 3 7.5 Tcl "Tcl Library Procedures"
.so man.macros
.BS
.SH NAME
Tcl_LinkArray, Tcl_LinkVar, Tcl_UnlinkVar, Tcl_UpdateLinkedVar \- link Tcl variable to C variable
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
int
\fBTcl_LinkVar\fR(\fIinterp, varName, addr, type\fR)
.sp
.VS "TIP 312"
int
\fBTcl_LinkArray\fR(\fIinterp, varName, addr, type, size\fR)
.VE "TIP 312"
.sp
\fBTcl_UnlinkVar\fR(\fIinterp, varName\fR)
.sp
\fBTcl_UpdateLinkedVar\fR(\fIinterp, varName\fR)
.SH ARGUMENTS
.AS Tcl_Interp varName in
.AP Tcl_Interp *interp in
Interpreter that contains \fIvarName\fR.
Also used by \fBTcl_LinkVar\fR to return error messages.
.AP "const char" *varName in
Name of global variable.
.AP void *addr in
Address of C variable that is to be linked to \fIvarName\fR.
.sp
.VS "TIP 312"
In \fBTcl_LinkArray\fR, may be NULL to tell Tcl to create the storage
for the array in the variable.
.VE "TIP 312"
.AP int type in
Type of C variable for \fBTcl_LinkVar\fR or type of array element for
\fBTcl_LinkArray\fR.  Must be one of \fBTCL_LINK_INT\fR,
\fBTCL_LINK_UINT\fR, \fBTCL_LINK_CHAR\fR, \fBTCL_LINK_UCHAR\fR,
\fBTCL_LINK_SHORT\fR, \fBTCL_LINK_USHORT\fR, \fBTCL_LINK_LONG\fR,
\fBTCL_LINK_ULONG\fR, \fBTCL_LINK_WIDE_INT\fR,
\fBTCL_LINK_WIDE_UINT\fR, \fBTCL_LINK_FLOAT\fR, \fBTCL_LINK_DOUBLE\fR,
\fBTCL_LINK_BOOLEAN\fR, or one of the extra ones listed below.
.sp
In \fBTcl_LinkVar\fR, the additional linked type \fBTCL_LINK_STRING\fR may be
used.
.sp
.VS "TIP 312"
In \fBTcl_LinkArray\fR, the additional linked types \fBTCL_LINK_CHARS\fR and
\fBTCL_LINK_BYTES\fR may be used.
.VE "TIP 312"
.sp
All the above for both functions may be
optionally OR'ed with \fBTCL_LINK_READ_ONLY\fR to make the Tcl
variable read-only.
.AP size_t size in
.VS "TIP 312"
The number of elements in the C array. Must be greater than zero.
.VE "TIP 312"
.BE
.SH DESCRIPTION
.PP
\fBTcl_LinkVar\fR uses variable traces to keep the Tcl variable
named by \fIvarName\fR in sync with the C variable at the address
given by \fIaddr\fR.
Whenever the Tcl variable is read the value of the C variable will
be returned, and whenever the Tcl variable is written the C
variable will be updated to have the same value.
\fBTcl_LinkVar\fR normally returns \fBTCL_OK\fR;  if an error occurs
while setting up the link (e.g. because \fIvarName\fR is the
name of array) then \fBTCL_ERROR\fR is returned and the interpreter's result
contains an error message.
.PP
.VS "TIP 312"
\fBTcl_LinkArray\fR is similar, but for arrays of fixed size (given by
the \fIsize\fR argument). When asked to allocate the backing C array
storage (via the \fIaddr\fR argument being NULL), it writes the
address that it allocated to the Tcl interpreter result.
.VE "TIP 312"
.PP
The \fItype\fR argument specifies the type of the C variable,
or the type of the elements of the C array,
and must have one of the following values, optionally OR'ed with
\fBTCL_LINK_READ_ONLY\fR:
.TP
\fBTCL_LINK_INT\fR
.
The C variable, or each element of the C array, is of type \fBint\fR.
Any value written into the Tcl variable must have a proper integer
form acceptable to \fBTcl_GetIntFromObj\fR;  attempts to write
non-integer values into \fIvarName\fR will be rejected with
Tcl errors. Incomplete integer representations (like the empty
string, '+', '-' or the hex/octal/decimal/binary prefix) are accepted
as if they are valid too.
.TP
\fBTCL_LINK_UINT\fR
.
The C variable, or each element of the C array, is of type \fBunsigned int\fR.
Any value written into the Tcl variable must have a proper unsigned
integer form acceptable to \fBTcl_GetWideIntFromObj\fR and in the
platform's defined range for the \fBunsigned int\fR type; attempts to
write non-integer values (or values outside the range) into
\fIvarName\fR will be rejected with Tcl errors. Incomplete integer
representations (like the empty string, '+', '-' or the hex/octal/decimal/binary
prefix) are accepted as if they are valid too.
.TP
\fBTCL_LINK_CHAR\fR
.
The C variable, or each element of the C array, is of type \fBchar\fR.
Any value written into the Tcl variable must have a proper integer
form acceptable to \fBTcl_GetIntFromObj\fR and be in the range of the
\fBchar\fR datatype; attempts to write non-integer or out-of-range
values into \fIvarName\fR will be rejected with Tcl errors. Incomplete
integer representations (like the empty string, '+', '-' or the
hex/octal/decimal/binary prefix) are accepted as if they are valid too.
.RS
.PP
.VS "TIP 312"
If using an array of these, consider using \fBTCL_LINK_CHARS\fR instead.
.VE "TIP 312"
.RE
.TP
\fBTCL_LINK_CHARS\fR
.VS "TIP 312"
The C array is of type \fBchar *\fR and is mapped into Tcl as a string.
Any value written into the Tcl variable must have the same length as
the underlying storage. Only supported with \fBTcl_LinkArray\fR.
.VE "TIP 312"
.TP
\fBTCL_LINK_UCHAR\fR
.
The C variable, or each element of the C array, is of type \fBunsigned char\fR.
Any value written into the Tcl variable must have a proper unsigned
integer form acceptable to \fBTcl_GetIntFromObj\fR and in the
platform's defined range for the \fBunsigned char\fR type; attempts to
write non-integer values (or values outside the range) into
\fIvarName\fR will be rejected with Tcl errors. Incomplete integer
representations (like the empty string, '+', '-' or the hex/octal/decimal/binary
prefix) are accepted as if they are valid too.
.RS
.PP
.VS "TIP 312"
If using an array of these, consider using \fBTCL_LINK_BYTES\fR instead.
.VE "TIP 312"
.RE
.TP
\fBTCL_LINK_BYTES\fR
.VS "TIP 312"
The C array is of type \fBunsigned char *\fR and is mapped into Tcl
as a bytearray.
Any value written into the Tcl variable must have the same length as
the underlying storage. Only supported with \fBTcl_LinkArray\fR.
.VE "TIP 312"
.TP
\fBTCL_LINK_SHORT\fR
.
The C variable, or each element of the C array, is of type \fBshort\fR.
Any value written into the Tcl variable must have a proper integer
form acceptable to \fBTcl_GetIntFromObj\fR and be in the range of the
\fBshort\fR datatype; attempts to write non-integer or out-of-range
values into \fIvarName\fR will be rejected with Tcl errors. Incomplete
integer representations (like the empty string, '+', '-' or the
hex/octal/decimal/binary prefix) are accepted as if they are valid too.
.TP
\fBTCL_LINK_USHORT\fR
.
The C variable, or each element of the C array, is of type \fBunsigned short\fR.
Any value written into the Tcl variable must have a proper unsigned
integer form acceptable to \fBTcl_GetIntFromObj\fR and in the
platform's defined range for the \fBunsigned short\fR type; attempts to
write non-integer values (or values outside the range) into
\fIvarName\fR will be rejected with Tcl errors. Incomplete integer
representations (like the empty string, '+', '-' or the hex/octal/decimal/binary
prefix) are accepted as if they are valid too.
.TP
\fBTCL_LINK_LONG\fR
.
The C variable, or each element of the C array, is of type \fBlong\fR.
Any value written into the Tcl variable must have a proper integer
form acceptable to \fBTcl_GetLongFromObj\fR; attempts to write
non-integer or out-of-range
values into \fIvarName\fR will be rejected with Tcl errors. Incomplete
integer representations (like the empty string, '+', '-' or the
hex/octal/decimal/binary prefix) are accepted as if they are valid too.
.TP
\fBTCL_LINK_ULONG\fR
.
The C variable, or each element of the C array, is of type \fBunsigned long\fR.
Any value written into the Tcl variable must have a proper unsigned
integer form acceptable to \fBTcl_GetWideIntFromObj\fR and in the
platform's defined range for the \fBunsigned long\fR type; attempts to
write non-integer values (or values outside the range) into
\fIvarName\fR will be rejected with Tcl errors. Incomplete integer
representations (like the empty string, '+', '-' or the hex/octal/decimal/binary
prefix) are accepted as if they are valid too.
.TP
\fBTCL_LINK_DOUBLE\fR
.
The C variable, or each element of the C array, is of type \fBdouble\fR.
Any value written into the Tcl variable must have a proper real
form acceptable to \fBTcl_GetDoubleFromObj\fR;  attempts to write
non-real values into \fIvarName\fR will be rejected with
Tcl errors. Incomplete integer or real representations (like the
empty string, '.', '+', '-' or the hex/octal/decimal/binary prefix) are
accepted as if they are valid too.
.TP
\fBTCL_LINK_FLOAT\fR
.
The C variable, or each element of the C array, is of type \fBfloat\fR.
Any value written into the Tcl variable must have a proper real
form acceptable to \fBTcl_GetDoubleFromObj\fR and must be within the
range acceptable for a \fBfloat\fR; attempts to
write non-real values (or values outside the range) into
\fIvarName\fR will be rejected with Tcl errors. Incomplete integer
or real representations (like the empty string, '.', '+', '-' or
the hex/octal/decimal/binary prefix) are accepted as if they are valid too.
.TP
\fBTCL_LINK_WIDE_INT\fR
.
The C variable, or each element of the C array, is of type \fBTcl_WideInt\fR
(which is an integer type
at least 64-bits wide on all platforms that can support it.)
Any value written into the Tcl variable must have a proper integer
form acceptable to \fBTcl_GetWideIntFromObj\fR;  attempts to write
non-integer values into \fIvarName\fR will be rejected with
Tcl errors. Incomplete integer representations (like the empty
string, '+', '-' or the hex/octal/decimal/binary prefix) are accepted
as if they are valid too.
.TP
\fBTCL_LINK_WIDE_UINT\fR
.
The C variable, or each element of the C array, is of type \fBTcl_WideUInt\fR
(which is an unsigned integer type at least 64-bits wide on all platforms that
can support it.)
Any value written into the Tcl variable must have a proper unsigned
integer form acceptable to \fBTcl_GetWideIntFromObj\fR (it will be
cast to unsigned);
.\" FIXME! Use bignums instead.
attempts to write non-integer values into \fIvarName\fR will be
rejected with Tcl errors. Incomplete integer representations (like
the empty string, '+', '-' or the hex/octal/decimal/binary prefix) are accepted
as if they are valid too.
.TP
\fBTCL_LINK_BOOLEAN\fR
.
The C variable, or each element of the C array, is of type \fBint\fR.
If its value is zero then it will read from Tcl as
.QW 0 ;
otherwise it will read from Tcl as
.QW 1 .
Whenever \fIvarName\fR is
modified, the C variable will be set to a 0 or 1 value.
Any value written into the Tcl variable must have a proper boolean
form acceptable to \fBTcl_GetBooleanFromObj\fR;  attempts to write
non-boolean values into \fIvarName\fR will be rejected with
Tcl errors.
.TP
\fBTCL_LINK_STRING\fR
.
The C variable is of type \fBchar *\fR.
If its value is not NULL then it must be a pointer to a string
allocated with \fBTcl_Alloc\fR.
Whenever the Tcl variable is modified the current C string will be
freed and new memory will be allocated to hold a copy of the variable's
new value.
If the C variable contains a NULL pointer then the Tcl variable
will read as
.QW NULL .
This is only supported by \fBTcl_LinkVar\fR.
.PP
If the \fBTCL_LINK_READ_ONLY\fR flag is present in \fItype\fR then the
variable will be read-only from Tcl, so that its value can only be
changed by modifying the C variable.
Attempts to write the variable from Tcl will be rejected with errors.
.PP
\fBTcl_UnlinkVar\fR removes the link previously set up for the
variable given by \fIvarName\fR.  If there does not exist a link
for \fIvarName\fR then the procedure has no effect.
.PP
\fBTcl_UpdateLinkedVar\fR may be invoked after the C variable has
changed to force the Tcl variable to be updated immediately.
In many cases this procedure is not needed, since any attempt to
read the Tcl variable will return the latest value of the C variable.
However, if a trace has been set on the Tcl variable (such as a
Tk widget that wishes to display the value of the variable), the
trace will not trigger when the C variable has changed.
\fBTcl_UpdateLinkedVar\fR ensures that any traces on the Tcl
variable are invoked.
.PP
Note that, as with any call to a Tcl interpreter, \fBTcl_UpdateLinkedVar\fR
must be called from the same thread that created the interpreter. The safest
mechanism is to ensure that the C variable is only ever updated from the same
thread that created the interpreter (possibly in response to an event posted
with \fBTcl_ThreadQueueEvent\fR), but when it is necessary to update the
variable in a separate thread, it is advised that \fBTcl_AsyncMark\fR be used
to indicate to the thread hosting the interpreter that it is ready to run
\fBTcl_UpdateLinkedVar\fR.
.SH "SEE ALSO"
Tcl_TraceVar(3)
.SH KEYWORDS
boolean, integer, link, read-only, real, string, trace, variable
